1. Field of the Invention
The present invention relates to an electromagnetic drive device in which a moving part supported to a stator moves at an inner side of the stator.
2. Description of the Related Art
There is known an electromagnetic drive device which directly supports a moving part at an inner peripheral side of a stator for reduction in the number of components and simplification the structure. In such an electromagnetic drive device, a coating portion is provided in at least one of the stator and the moving part for reducing hysteresis of the moving part at the time of power supply or non-power supply to a coil (refer to JP-A-2001-263524 or JP-A-2002-222710 corresponding to U.S. Pat. No. 6,806,802). The coating portion carries out lubrication between the stator and the moving part, which move relatively to each other while contacting to each other, and secures smooth movement of the moving part.
However, in a case of forming the coating portion at the stator or the moving part, relative movement between the stator and the moving part for a long period of time causes wear of the coating portion. Further, when the coating portion disappears due to the wear development, the magnetic body of the stator or the moving part is exposed. Therefore, disappearance of the coating portion rapidly increases a friction coefficient, which invites to the wear of the stator and the moving part. Accordingly, resistance to movement of the moving part increases to increase the hysteresis of the moving part. As a result, deterioration in controllability or interruption of the movement of the moving part may be caused.
In addition, in a case of increasing the thickness of the coating portion for extending a lifetime of the coating portion, a clearance between the stator and the moving part is enlarged due to development of the wear of the coating portion. Therefore, a moving force of the moving part is lowered.